CDRecorder - Here's a sample XS0X vs. XS0Z comparison with 40x Princo discs:
XS0Z @ 32x (P-CAV)
Burn time: 3:06
C1 Errors: Max - 228, Total - 55015, Avg. - 16.301
XS0X @ 32x (Z-CLV)
Burn time: 3:32
C1 Errors: Max - 30, Total - 9340, Avg. - 2.758
I'm willing to wait 26 extra seconds for an 83% lower C1 error rate. How pronounced the difference between the firmwares depends on quality of media used. But the relative quality difference (percentage wise) produced by the 2 firmwares is largely in XS0X's favor with the 6 or so different media brands I had on hand.
Let us know what you find after your own tests.